Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants are composed of gaseous compounds including, among other things, the oxides of nitrogen (NOX). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NOX emitted to the atmosphere by an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
In order to comply with the regulation of NOX, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR). SCR is a process where a reductant, most commonly urea ((NH2)2CO) or a water/urea solution, is selectively injected into the exhaust gas stream of an engine and absorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH3), which reacts with NOX in the exhaust gas to form water (H2O) and diatomic nitrogen (N2).
In some applications, the substrate used for SCR purposes may need to be very large to help ensure it has enough surface area or effective volume to absorb appropriate amounts of the ammonia required for sufficient reduction of NOX. These large substrates can be expensive and require significant amounts of space within the exhaust system. In addition, the substrate must be placed far enough downstream of the injection location for the urea solution to have time to decompose into the ammonia gas and to evenly distribute within the exhaust flow for the efficient reduction of NOX. This spacing may further increase packaging difficulties of the exhaust system.
An exemplary SCR-equipped system for use with a combustion engine is disclosed in JP Patent Publication No. 2008/274,851 (the '851 publication) of Makoto published on Nov. 13, 2008. This system includes an exhaust gas purification device having a gas accumulation canister, a separate dispersion canister, and a mixing pipe connected between edges of the gas accumulation and gas dispersion canisters. A particulate filter and an oxidation catalyst are disposed in the gas accumulation canister, while an SCR catalyst and ammonia reduction catalyst are disposed within the gas dispersion canister. A urea injector is located in the mixing pipe, upstream of the SCR catalyst.
Although compact in size, the exhaust system of the '851 patent may still be problematic. In particular, the multiple canisters used in the '851 system may increase component cost, packaging complexity, and an overall size of the system. In addition, the single SCR catalyst may be large and drive up the cost of the system.
The aftertreatment module of the present disclosure solves one or more of the problems set forth above and/or other problems of the prior art.